The present invention relates generally to an electromagnetic coil apparatus. More particularly, the present invention is concerned with an improved structure of the apparatus which is not affected by environmental factors.
An electromagnetic coil apparatus is often used in, for example, a hydraulic control circuit for controlling a hydraulic flow. A conventional electromagnetic coil apparatus is disclosed in FIGS. 4 and 5.
Referring now to FIG. 4, an electromagnetic coil apparatus 50 basically includes a coil bobbin 51, an electric coil 52, an electric terminal 53 and an outer housing 54. The coil bobbin 51 forms a center hole 51a and the electric coil 52 is wound on the coil bobbin 51. The electric coil 52 is comprised of an electric wire 52a having an electric wire end 52b which is molded into the outer housing 54. The outer housing 54 forms a cylindrical connecting portion 54a. A valve assembly (not shown), for example, may be arranged in the center hole 51a. The electric terminal 53 is molded into the coil bobbin 51 and the outer housing 54. The outer housing 54 is formed about the coil 52 and the coil bobbin 51 with the end 52b of the electric wire 52a molded into the outer housing as described above. A detailed view of the arrangement of the electric wire end 52b relative to the housing and the bobbin is shown in FIG. 5 which clearly shows the electric wire end 52b being molded completely within the outer housing 54.
In operation with a valve assembly, the electromagnetic coil apparatus 50 is generally subjected to vibrations and/or high temperature conditions. As a result, an expansion or contraction of the electric wire end 52b and the electric terminal 53 will occur. Therefore, serious problems are present with the above-described design. For example, if these operating conditions are maintained, the electric wire end 52b and/or the outer housing 54 may be damaged or broken. Once the electromagnetic coil apparatus 50 is broken, the normal operation will be prevented.